1. Field of the Invention
This invention relates to a combination insect extermination and illumination device and, particularly, to an electric circuit capable of concurrently operating both a device for killing insects by electrocution and a lamp providing both an insect luring light and continuous illumination of an area around the device.
2. Description of Related Art
Electrical devices for killing insects by electrocution have been known and sold commercially. These devices incorporate a high voltage electrocution grid and a low power light source means for attracting the insects both of which are mounted in a suitable housing. The typical insect exterminator light source is of a form primarily designed to attract insects and while some illumination is produced, such illumination is at a relatively low level. Existing electric insect exterminators generally utilize lighting means in the form of relatively low power fluorescent tubes and a ballast transformer which controls the current flowing through the fluorescent tubes. For example, the apparatus for electrically exterminating insects of De Yoreo (U.S. Pat. No. 4,182,069), the electric insect trap of Hamid et al. (U.S. Pat. No. 3,935,662) and the electric insect killer of Hedstrom (U.S. Pat. No. 4,248,005) utilize such an arrangement. Other devices, for example the insect exterminator of Rittenhouse (U.S. Pat. No. 1,982,123), have been designed to incorporate a simple incandescent filament lamp fixture which is powered independently of the electrocution device circuitry. Such illumination arrangements are sufficient for attracting insects; however, these prior art arrangements do not provide relatively high level illumination and therefore one or more additional lighting fixtures such as a mercury vapor lamp need to be used concurrently with the exterminating device when a relatively high level of illumination is needed at the site of the device, whether in an indoor or outdoor environment.
The insect exterminator of Folmer et al. (U.S. Pat. No. 1,962,439) teaches the use of a mercury vapor lamp. The use of such a lamp is attractive as a mercury vapor bulb provides the benefit of an ultraviolet light which has been known to attract insects. In addition, the mercury vapor bulb has a long service life and produces a high level of light output. Additional useful background information on the relation of light wave length to attracting insects can be found in U.S. Pat. Nos. 3,540,145 and 4,157,629.
Unlike a fluorescent lamp, it is a characteristic of a mercury vapor lamp that, after the bulb is energized, several minutes must elapse before normal operation is reached. This peculiar characteristic of the mercury vapor lamp, even though more desirable from the viewpoint of attracting insects and providing substantial and efficient illumination, presents difficulties in incorporating such a lamp with a transformer operated electric insect exterminator. In such a device, an electrocution of an insect normally causes a disturbance in the magnetic flux which propagates in the circuit. In the absence of means for offsetting the effect of such disturbance, such disturbance will cause an interruption in the light output of the mercury vapor lamp each time an insect is electrocuted. In order to avoid this problem, Folmer's insect exterminator circuit incorporates two independent transformers so as to operate the lamp and the electrocution grid separately. Although Folmer's invention is capable of providing a constant light output, such a device which utilizes two separate transformers as a practical device is heavy, cumbersome and expensive. It would therefore be preferred to have a device which utilizes a single transformer to concurrently and continuously operate both an electrocution grid and a lamp and to have the lamp serve as both an insect luring light and a source of continuous illumination for the area where the device is located.
Single transformers which are capable of operating two separate loads are generally known though not in the form of the present invention. For example, the electric insect killer of Hedstrom (U.S. Pat. No. 4,248,005) teaches a circuit which utilizes a single transformer to operate both the electrocution grid and a pair of insect-attractive fluorescent lamps. The described circuit however permits the collapse of the magnetic field following an electrocution. Furthermore, if such a circuit were to be integrated in a circuit to concurrently operate both an electrocution grid and a mercury vapor lamp, this would inevitably lead to several minutes of interruption in the light output whenever an electrocution occurred during which interruption, the mercury vapor in the lamp would condense. Useful related transformer background information is also to be found in U.S. Pat. Nos. 3,061,759 and 3,919,595.
A single-primary, dual-secondary coil transformer having all of the electrical coils wound on a common core is disclosed in U.S. Pat. No. 2,558,293 to Feinberg as a part of an apparatus for starting and operating gaseous discharge devices. However, in the Feinberg-type circuit, an intimate interconnection of the coils and loads does not allow for the operation of two independent non-interacting devices, such as an electrocution grid and a lamp. A somewhat similarly structured transformer is taught in U.S. Pat. No. 4,943,763 to Bobry. Although the transformer shown in the Bobry patent provides for the operation of two independent, non-interacting devices, its ferroresonant manner of operation is unsuitable for the operation of a device of the character herein described.
Reference is also made for background purposes to U.S. Pat. No. 4,422,015 to Nilsen in which a single transformer is illustrated as driving both a fluorescent lamp for attracting insects and an insect destruction grid. However, in the '015 patent, the secondary coils driving the lamp and electrocution grid, unlike the present invention, are not mounted on the same transformer leg as the leg on which the primary coil is mounted. The '015 patent transformer thus causes the primary coil flux to split into two substantially equal components one linking the lamp secondary drive coil and the other linking the electrocution grid drive coil. The present invention recognizes two undesirable consequences of the '015 patent transformer-winding arrangement. First, the reduction in flux in each secondary coil requires a proportionate increase in number of turns required, leading to increases in both cost and losses. Second, a disturbance in the high voltage circuit tends to disturb the lamp circuit thus defeating isolation as obtained by the present invention.